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1.1 mil millón kilómetros!

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Betelgeuse

Betelgeuse is a red supergiant star in the constellation Orion, and the closest red supergiant to Earth. A 2020 study estimated that it is about 1.1 billion kilometers across, roughly 760 times the width of the Sun. That figure is the width of the star's visible surface, and it is uncertain because the star's distance is not known precisely.

Size

Stars have no solid surface, and Betelgeuse's size is estimated from two things: how wide it looks in the sky and how far away it is. Its apparent width has been measured precisely with interferometry, which combines light from several telescopes. It is about 42 thousandths of an arcsecond, where an arcsecond is 1/3,600 of a degree. That is the width of a human hair seen from about 490 meters away.

The distance is harder to pin down. In 2020 a team led by Meridith Joyce used computer models of how Betelgeuse pulsates to estimate its radius at 764 times the Sun's. That gives a width of about 1.06 billion kilometers, within a range of 0.98–1.22 billion, and puts the star about 550 light-years away (a light-year is the distance light travels in one year). Other estimates place it farther, around 650 light-years, and at that distance the same apparent width would mean a star about 1.3 billion kilometers across.

Betelgeuse is also a variable star. It pulsates in a cycle of about 400 days, so its surface moves and its brightness changes. Beyond the visible surface, it has a vast, extended outer atmosphere.

Size comparisons

  • Betelgeuse is about 760 times as wide as the Sun, which is about 1.39 million kilometers across.
  • If Betelgeuse took the Sun's place, its surface would reach past the orbit of Mars, about two-thirds of the way to the orbit of Jupiter.
  • More than 400 million Suns could fit inside it, by volume.
  • Antares, the next smaller star in the explorer and another red supergiant, is about 680 times as wide as the Sun, so Betelgeuse is about one-tenth wider.
  • If the Sun were shrunk to the size of a basketball, Earth would be a 2-millimeter bead 26 meters away, and Betelgeuse would be a ball about 180 meters across.

The 2019 dimming

In late 2019 Betelgeuse grew noticeably fainter, and the dimming lasted a few months. Observations with the Hubble Space Telescope and other observatories showed why. The star had blown off a large part of its visible surface in 2019, in a huge eruption called a surface mass ejection. The material weighed several times as much as the Moon, about 400 billion times as much as a typical eruption from the Sun.

As the material moved away from the star, it cooled into a cloud of dust that blocked some of the starlight. The outburst also interrupted the 400-day pulsation that astronomers had followed for almost 200 years. Betelgeuse is expected to end its life as a supernova, an exploding star, but the astronomers who studied the outburst concluded that it was not necessarily a sign that the explosion was near.

A hidden companion

In 2025 astronomers announced the first likely sighting of a small companion star, using the Gemini North telescope. They named it Siwarha, which means "her bracelet." It circles Betelgeuse about every six years, passing through the supergiant's vast outer atmosphere. Next to Betelgeuse it is tiny.

In January 2026, astronomers reported a trail of dense gas that the companion leaves as it moves through Betelgeuse's outer atmosphere. In July 2026, the European Southern Observatory released the clearest image of the companion yet, taken with its Very Large Telescope. The image suggests the companion has two to three times the Sun's mass. It will next be easiest to see in November 2027.

Sources

La Escala del Universo > Betelgeuse

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